Vehicle air suspension having a lifting system

ABSTRACT

There is disclosed a vehicle air suspension of the trailing arm type in which a system for lifting one or more road wheels whose load-bearing capacity is not required comprises a cradle having a platform member on which is supported an air bag. The air bag is disposed, on inflation, to act on a longitudinal member of the suspension so as to urge that member, and a road wheel attached thereto, upwardly. The cradle has a pair of arms which pass to opposite sides of the longitudinal member. Embodiments are disclosed in which the arms are adapted to be secured to a suspension damper mounting, to a pivot of the longitudinal member, or to a suspension bracket of the vehicle.

The present invention relates to a vehicle air suspension system havinga lifting system for lifting one or more road wheels of the vehicle.

BACKGROUND OF INVENTION

The air suspension to which this invention is applicable typicallycomprises a bracket secured to and depending from a chassis member ofthe vehicle, a longitudinal member extending generally lengthwise of thevehicle which is mounted on the bracket for pivoting about an axisgenerally transverse of the vehicle and which carries an air springrearwards of the axis so that the air spring acts between the vehicleand the longitudinal member. A stub axle for rotatably mounting a wheelis secured to the member rearwards of the axis. Alternatively, thesuspension may comprise two brackets, one depending from each side ofthe vehicle, each bracket having a longitudinal member extendinggenerally lengthwise of the vehicle and which is mounted to the bracketfor pivoting about an axis generally transverse of the vehicle and whichcarries an air spring rearwards of said front end portion so that theair springs act between the respective longitudinal members and thevehicle. An axle on which is carried two or more road wheels extendsbetween and beyond the longitudinal members and is secured theretorearwards of said front end portions. Such air suspensions are hereafterreferred to as air suspensions of the type described.

Vehicles equipped with an air suspension of the type described areadvantageously provided with a lifting system to lift road wheels out ofcontact with the road surface when their load-carrying capacity is notrequired, so as to reduce wear of tires and other suspension components.Typically the system will operate to lift a pair of wheels on oppositesides of the vehicle, these wheels either being mounted on a common axleor mounted independently on stub axles.

An example of an air suspension system of the type described having alifting system is disclosed in EP-A-0 431 673. The lifting systemcomprises an air bag which is supported on a bracket fixed below alongitudinal member of the suspension, inflation of the air bag urgingthe longitudinal member upwardly. The system has disadvantages in thatthe bracket must be welded to a part of the vehicle chassis and a memberhas to be provided connected between the upper end of the air bag andthe longitudinal member at its connection to the axle to control thelocus of the top of the air bag.

SUMMARY OF INVENTION

The aim of the present invention is to provide an air suspension havinga lifting system which may be fitted to a vehicle with a minimum ofeffort, either as original equipment or as a retro-fit suitable forsuspensions made by different manufacturers and of different designs.

According to a first of its aspects, the invention provides an airsuspension system for a vehicle comprising a longitudinal memberextending generally lengthways of the vehicle and mounted to the vehiclefor pivotal movement about an axis generally transverse of the vehicle,an air spring disposed to act between the longitudinal member rearwardsof the axis and the vehicle, and a road wheel carrier disposed on thelongitudinal member rearwards of the axis, wherein the suspension systemfurther comprises a lifting system for lifting at least one wheel of thevehicle comprising a cradle having a platform member and two arms eacharm connecting the platform member to the vehicle, the arms beingdisposed to opposite sides of the longitudinal member, the liftingsystem further comprising an air bag disposed to act between theplatform member and the longitudinal member such that inflation of theair bag causes upward pivoting movement of the longitudinal member, soraising the or each wheel connected thereto.

(It is to be understood that the term "air bag" as used herein is notintended to be construed narrowly and should be taken to includebellows, air springs, and so forth.)

By supporting the platform member at opposite sides of the longitudinalmember, undesirable twisting and bending stresses within the cradle maybe reduced, consequentially reducing the strength required of itsindividual components.

The air suspension system of the present invention may be embodied as anindependent system in which pairs of wheels at opposite sides of thevehicle are carried on individual stub axles. Alternatively, it may beapplied to a conventional system in which pairs of wheels on oppositesides of the vehicle are carried on a common, rigid axle.

The lifting system preferably comprises anchorage means to secure alower part of the air bag to the platform member.

Advantageously, the lifting system additionally comprises coupling meansby which an upper part of the air bag is connected to the longitudinalmember. More preferably, the coupling means substantially preventsrelative movement between an upper surface of the air bag and thelongitudinal member.

Alternatively or additionally the lifting system may further comprisesguide means interconnecting an upper part of the air bag and the cradleand operable to constrain movement of an upper portion of the air bag towithin a desired path. In a preferred embodiment, the guide means maycomprise a beam, end portions or end fittings of which are constrainedto travel within guides or slots in the arms or along the arms of thecradle.

The system may further comprise bearing means, such as a block ofrubber, or plastics material to mechanically interconnect the air bagand the longitudinal member on inflation of the air bag. The bearingmeans may be part of, integral with, or disposed close to the couplingmeans.

Typically, in air suspension systems of the type described, thelongitudinal member is connected to the vehicle by a pivot, which maycomprise a pivot bolt extending along the pivotal axis. Advantageously,the cradle is adapted for connection to the or to part of the pivot. Acradle of this type is particularly adapted for use in cases where anair suspension system of the type described is to be provided with alifting system after manufacture, or where attachment of the cradle bywelding would not be convenient.

From a second of its aspects the invention provides an air suspensionsystem for a vehicle comprising a longitudinal member extendinggenerally lengthways of the vehicle and mounted to the vehicle forpivotal movement about an axis generally transverse of the vehicle, anair spring disposed to act between the longitudinal member rearwards ofthe axis and the chassis, a road wheel carrier disposed on thelongitudinal member rearwards of the axis, and a suspension damperconnected (directed or indirectly) between the longitudinal member andthe vehicle, the suspension system further comprising a lifting systemfor lifting at least one wheel of the vehicle comprising a cradleadapted for connection to the said mounting means and an air bagsupported by the cradle and arranged, on inflation thereof, to urge thelongitudinal member upwardly, so raising the wheel carrier.

This aspect of the invention, by making use of a suspension dampermounting means, minimises the amount of additional work and apparatusrequired where a pre-existing air suspension system is to be providedwith a lifting system. It may particularly be used for after-marketconversion of an existing suspension system.

In suspension systems in which the damper is connected to the vehicle(directly or indirectly) by a pivot bolt, the cradle may conveniently beprovided with supporting members having holes through Which the pivotbolt passes.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described in detail by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a cradle being a part of a firstembodiment of the invention carried by a suspension bracket and alsoshowing part of a longitudinal member of the suspension;

FIG. 2 is similar to FIG. 1 but seen from the opposite end and includesan air bag and clamp;

FIG. 3 is a side view of the suspension system of the embodiment of theinvention;

FIG. 4 is a view of an air bag and a lower half clamp being parts of thefirst embodiment of the invention;

FIG. 5 is a scrap view of a clamp on a longitudinal member of thesuspension of the first embodiment;

FIG. 6 is a perspective view of a platform member being a part of asecond embodiment of the invention; and

FIG. 7 shows an alternative cradle with air bag and constraint, beingparts of a third embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIGS. 1 to 5, an air suspension system of a vehiclecomprises a bracket 10 (shown schematically in FIGS. 1 and 2) fixed to achassis of the vehicle (not shown). The bracket 10 has first and secondside members 12,14 which depend from the chassis, and a vertical frontplate 16 interconnecting the side members 12,14 at their extremitiesforemost on the vehicle. The bracket 10 thus has a box-likeconstruction, open to its rear and to below. At the rear, the peripheryof each of the side members 12,14 has a lower portion which extends fromclose to the top of the bracket 10 downwardly and rearwardly of thebracket 10, each of these portions having a flange 18,20 projectinglaterally therefrom.

A longitudinal member 22 is connected within the bracket 10 to a pivotof conventional form comprising a pivot bolt 24 passing through spigots25 which project laterally from each side member 12,14 of the bracket10. The pivot permits movement of the longitudinal member 22 about ahorizontal axis towards its forward end.

From the pivot 24, the longitudinal member 22 extends rearwardly, beingconnected at a rear end portion to an air spring 26. The air spring 26is also connected to the chassis, and acts as a compression springbetween the longitudinal member 22 and the chassis.

Between the pivot 24 and the air spring 26, an axle 28 of the vehicle issecured to the longitudinal member 22 by a clamp 30.

A telescopic suspension damper 32 interconnects the axle 28 and thebracket 10. The damper 32 has first and second mounting eyes througheach of which a bolt may be passed to secure the damper 32 to asuspension component. The first eye is secured to the clamp 30 by a bolt34. The second eye is secured to the bracket 10, the eye engaging withone of a pair of lugs 36 projecting therefrom, a bolt 38 passing throughthe lug 36 and the eye 38 to secure the damper 32.

A cradle 40 depends from the bracket 10. The cradle 40 comprises a pairof arms 42,44 and a base member 46.

Each arm 42,44 has an upper plate portion 50 through which there is acircular aperture. The lugs 36 of the bracket 10 each extends throughthe aperture of a respective arm, the arms being secured by the pivotbolt 38 and a cooperating nut.

Each arm 42,44 further comprises a lower portion 52 which depends fromthe respective upper portion 50, and is connected thereto by a steppedportion 54. The stepped portion 54 displaces the lower portion 52 withrespect to the corresponding upper portion 50 outwardly from the bracket10. Each stepped portion 54 abuts a corresponding flange 20 of thebracket 10 for resisting pivotal movement of the cradle 40 in adirection of rearward movement of the lower portions 52 of the arms. Alug 56 projects from each arm to engage a respective flange 20 to resistpivoting movement of the cradle in the opposite direction.

The base member 46 interconnects lower portions 52 of the arms 42,44remote from the upper portions 50. The base member 46 is attached as bywelding to each of the arms 42,44. The base member 46 constitutes aplatform member of the cradle 40. In an alternative configuration, theplatform member may comprise a pair of base members each attached as bywelding to one of the arms 42,44, and by engagement with a slot in theother, such that the two arms 42,44 may be separated from one another tofacilitate mounting of the cradle 40.

An air bag 60 is supported on the platform member and extends to thelongitudinal member 22. The air bag 60 is secured to the platform memberby a plurality of bolts which extend through apertures 62 in theplatform member to engage with a lower part of the air bag 60, and toconstitute anchorage means for the air bag.

The air bag 60 is secured to the longitudinal member 22 by a clamp 64.The clamp 64 (which is shown in detail in FIGS. 4 and 5) comprises upperand lower clamp members 66,68, and constitutes coupling means for theair bag.

The upper clamp member 66 comprises a metal strap 70 which extendsacross the longitudinal member 22. End portions of the strap 70 whichproject laterally beyond the longitudinal member 22 are displaceddownwardly towards the lower clamp member 68 and are each provided witha through hole. A pair of strengthening flanges 72 projectperpendicularly from the strap 70. A pad 74 of hard rubber is disposedbetween the strap 70 and the longitudinal member 22, the pad 74 being aclose fit between the strap 70 and the longitudinal member 22.

The lower clamp member 68 comprises a strap 76 having through holes 77,a pad and strengthening flanges 78 of similar configuration to those ofthe upper clamp member 66, these components being in an inverteddisposition to engage a lower surface of the longitudinal member 22. Thebase of the lower clamp member 68 acts as a bearing means formechanically interconnecting the air bag 60 and the longitudinal member22 and to transmit force therebetween on inflation of the air bag 60.The lower clamp member 68 is secured to a mounting plate 80 havingapertures through which bolts pass to secure the plate 80 to the top ofthe air bag 60.

A central portion 82 of the plate 80 is upstanding from the air bag 60and on this portion 82 the strap 76 is supported. The intermediateportions 84 of the plate 80 adjoin the central portion 80 and areperpendicular thereto. The intermediate portions 84 abut inner surfacesof the strengthening flanges 78.

The upper and lower clamp members are secured together by bolts 86passing through the apertures 77 and associated nuts 88 so as to clampsecurely the longitudinal member 22 between themselves. Thissubstantially eliminates longitudinal or transverse movement between thelongitudinal member and the top of the air bag 60.

In a vehicle suspension system, an arrangement as described above istypically provided adjacent both ends of the axle 28. In the case of avehicle with independent suspension, the axle 28 is replaced with a pairof stub axles on opposite sides of the vehicle, each provided with anarrangement as described above, and each of which carries one or moreroad wheels.

In use, when an axle 28 of a vehicle is to be raised, air pressure isremoved from each air spring 26 associated with that axle 28. Airpressure is then applied to each air bag 60 associated with the axle 28,causing the air bags 60 to expand. The lower end of each air bag 60 issecured to the platform of the respective cradle 40 and so cannot movedownwards. Thus, upwardly-directed force is applied through therespective clamp 64 and pad to the longitudinal member 22, so causingthe longitudinal member 22 to pivot upwardly, raising the axle 28 as itdoes so. Operation of the system on an independently suspended vehicleis similar, with, each of a pair of stub axles being raisedsimultaneously.

With reference now to FIG. 6, there is shown an alternative cradle 100for use in a second embodiment of the invention mounted on a suspensionbracket 10 as described above.

The cradle 100 of the second embodiment comprises a platform 102 onwhich an air bag (not shown) may be supported. The platform 102 issurrounded by an upwardly directed flange 104, two portions of which areformed as upwardly extending lugs 106. Each lug 106 has an aperturethrough which passes a respective spigot or location collar 25 of thesuspension bracket 10. A further portion of the flange 104 to the frontof the cradle 100 engages with a lower surface of the bracket 10 toresist pivotal movement of the cradle 100 about the axis of the spigots25.

In this embodiment, an air bag acts between the platform 102 and alongitudinal member of the suspension (not shown) to lift that member ina manner substantially similar to that described above in relation tothe first embodiment, including a clamp as 64.

With reference to FIG. 7, a lifting system of a third embodiment of theinvention comprises a cradle 120 comprising a pair of side members122,124 between lower portions of which extends a platform member 126which may be constructed in a manner similar to the platform member ofthe cradle 40 of the first embodiment described above.

Upper end portions 128,130 of the side members 122,124 extendhorizontally towards one another, upper portions of each member being aninverted `L` shape in profile.

A cross member 132 is secured to lower surfaces of each upper endportion 128,130 by bolts extending through holes 134 in the cross member132 and upper end portions 128,130.

Each side member 122,124 has a slot 134 passing through it. Each slot134 has a substantially vertical lower portion and an upper portionwhich curves towards the front of the vehicle.

A beam 136 extends transversely of the cradle 120, the beam carrying onan upper surface centrally a block of rubber 138 as bearing means. Ateach end of the beam 138 there is secured an arm 140 on which is carrieda shaft 142 which extends through a slot in a respective arm 122,124.Each shaft 142 carries inner and outer guide rollers 144,146 disposed onopposite sides of each arm 122,124. Alternatively, the beam may beprovided with means which engage outer surfaces of the arm, and areguided thereby.

An air bag 146 is secured to the platform member 126 and to the beam136, inflation of the air bag 146 causing the beam 136 to travelupwardly (its path being guided by the shafts 142 in the slots 134,thereby restraining movement of an upper part of the air bag 146 to apath defined by the slots 134.

In use, the cradle is secured (for example, by welding) to a bracket ofa vehicle suspension, as described above. A longitudinal member 22 ofthe suspension passes through the cradle between the beam 136 and thecross member 132. On inflation of the air bag 146 the beam 136 movesupwards, the rubber block 138 engaging a lower surface of thelongitudinal member 22, whereupon further inflation of the air bagcauses the longitudinal member 22 and a road wheel attached thereto tomove upwards.

I claim:
 1. An air suspension system for a vehicle comprising alongitudinal member extending generally lengthways of the vehicle andmounted to the vehicle for pivotal movement about an axis generallytransverse of the vehicle, an air spring disposed to act between thelongitudinal member rearwards of the axis and the vehicle, and a roadwheel carrier disposed on the longitudinal member rearwards of the axis,wherein the suspension system further comprises a lifting system forlifting at least one wheel of the vehicle comprising a cradle having aplatform member and two arms each arm connecting the platform member tothe vehicle, the arms being disposed to opposite sides of thelongitudinal member, the lifting system further comprising an air bagdisposed to act between the platform member and the longitudinal membersuch that inflation of the air bag causes upward pivoting movement ofthe longitudinal member, so raising the or each wheel connected thereto.2. An air suspension system according to claim 1 in which the road wheelcarrier comprises a stub axle on which one or more wheels is carried, asimilar suspension system being provided for opposite wheels on left andright sides of the vehicle.
 3. An air suspension system according toclaim 1 in which the road wheel carrier comprises an axle extendingtransversely of the vehicle, to carry road wheels for left and rightsides of the vehicle.
 4. An air suspension system according to claim 1further comprising anchorage means by which a lower part of the air bagis secured to the platform member.
 5. An air suspension system accordingto claim 1 further comprising coupling means by which an upper part ofthe air bag is connected to the longitudinal member.
 6. An airsuspension system according to claim 5 in which the coupling meanssubstantially prevents relative movement between an upper surface of theair bag, and the longitudinal member.
 7. An air suspension systemaccording to claim 1 further comprising guide means interconnecting anupper part of the air bag and the cradle and operable to constrainmovement of an upper portion of the air bag relative to the cradle to adesired path.
 8. An air suspension system according to claim 7 in whichthe guide means comprises a beam having end portions or end fittings,and the arms of the cradle have guides or slots within which the endportions or end fittings are constrained to travel.
 9. An air suspensionsystem according to claim 1 having bearing means disposed tomechanically interconnect the air bag and the longitudinal member oninflation of the air bag.
 10. An air suspension system according toclaim 9 in which the bearing means comprises a block of rubber orplastics material.
 11. An air suspension system according to claim 1further comprising pivot means by which the longitudinal member issecured to the vehicle, the cradle being adapted for connection to thepivot means.
 12. An air suspension system according to claim 11 in whichthe pivot means comprises a pivot bolt extending along the transverseaxis about which the longitudinal member pivots, the arms of the cradlehaving holes through which the pivot bolt extends.
 13. An air suspensionsystem according to claim 11 in which the pivot means comprises a pivotbolt extending along the transverse axis about which the longitudinalmember pivots, the arms of the cradle having holes through which thepivot bolt extends, and the cradle carrying stop means to resist itspivoting about the pivot bolt.
 14. An air suspension system according toclaim 1, further comprising a suspension damper connected to thelongitudinal member and, by pivot means, to the vehicle, the cradlebeing connected to the vehicle by the pivot means.
 15. An air suspensionsystem according to claim 14 in which the pivot means comprises a pivotbolt, the arms of the cradle having holes through which the pivot boltextends.
 16. An air suspension system for a vehicle comprising alongitudinal member extending generally lengthways of the vehicle andmounted to the vehicle for pivotal movement about an axis generallytransverse of the vehicle, an air spring disposed to act between thelongitudinal member rearwards of the axis and the chassis, a road wheelcarrier disposed on the longitudinal member rearwards of the axis, and asuspension damper connected to the longitudinal member and, by mountingmeans, to the vehicle, the suspension system further comprising alifting system for lifting at least one wheel of the vehicle comprisinga cradle adapted for connection to the said mounting means and an airbag supported by the cradle and arranged, on inflation thereof, to urgethe longitudinal member upwardly, so raising the wheel carrier.
 17. Anair suspension system according to claim 16 in which the mounting meanscomprises a pivot element, the cradle having members through which thepivot element extends.